Press Brake Bending Calculator
Instantly calculate bending force, internal radius, minimum flange and V-die opening for any CNC press brake setup. Supports mild steel, stainless steel, aluminum and high-strength steel. For the underlying formulas, see our press brake tonnage calculation guide.
F = (1.54 × Rm × S² × L) / (V × 1000) [kN]
Ri = V × material factor | Bmin = V × 0.656
Quick Answer: How much press brake tonnage do I need?
A press brake should have more rated tonnage than the calculated bending force. For production work, Rucheng normally recommends adding a 20-30% reserve above the calculated requirement, then checking bend length, frame rigidity, tooling, V-die opening, material grade and available workshop power before choosing the final machine.
How to Calculate Press Brake Bending Parameters
Bending Force Formula (DIN Standard)
F = 1.54 × Rm × S² × L / (V × 1000) [kN]
- F — Bending force (kN)
- Rm — Material tensile strength (MPa): S235=360, S275=430, SS304=700, AL=210
- S — Sheet thickness (mm)
- L — Bend length (mm)
- V — V-die opening (mm), optimal = 8×S
| Thickness (S) | V-Die (V) | Force (kN) | Force (tons) | Ri (mm) | B min (mm) |
|---|---|---|---|---|---|
| 1 mm | 8 mm | 132 kN | 13.5 T | 1.0 | 5.2 |
| 2 mm | 16 mm | 331 kN | 33.7 T | 2.0 | 10.5 |
| 3 mm | 24 mm | 496 kN | 50.6 T | 3.0 | 15.7 |
| 4 mm | 32 mm | 661 kN | 67.4 T | 4.0 | 21.0 |
| 6 mm | 48 mm | 992 kN | 101 T | 6.0 | 31.5 |
| 8 mm | 64 mm | 1323 kN | 135 T | 8.0 | 42.0 |
| 10 mm | 80 mm | 1654 kN | 169 T | 10.0 | 52.5 |
How to use the result for machine selection
- Use the calculated force as the minimum required bending force for this one bend.
- Add the selected safety margin before choosing machine tonnage.
- Check whether the bend uses the full machine length or only a short section.
- Confirm the V-die opening, minimum flange and inside radius from the actual drawing, then match the result with a standard CNC bending machine mold or special tooling.
- For stainless steel or high-strength steel, leave extra reserve for springback and tooling wear.
Information needed for a press brake quote
- Material grade and tensile strength.
- Thickness range and maximum bend length.
- Part drawings with bend angles, flange length and inside radius.
- Annual production quantity and accuracy requirement.
- Preferred controller, back gauge axes, crowning and tooling requirements, including whether the part needs a large-radius arc mold.
Material and V-die selection notes
| Material | Starting V-die rule | Machine selection note |
|---|---|---|
| Mild steel | V = 8 × thickness | Use the calculator result plus normal production reserve. |
| Stainless steel | V = 8-10 × thickness | Needs more force and more springback compensation than mild steel. |
| Aluminum | V = 8 × thickness or larger | Check alloy temper and minimum radius to avoid cracking; use an arc mold when the drawing requires a smooth large radius. |
| High-strength steel | V = 12-13 × thickness | Choose a larger V-die and leave extra tonnage reserve. |
What is the optimal V-die opening for press brake bending?
The optimal V-die is 8× the material thickness for mild steel, stainless steel and aluminum. For high-strength steel (Weldox/Strenx 700+), use 12–13×. Example: 3mm mild steel → 24mm V-die. Too small a die increases force and cracking risk; too large gives an oversized radius.
How is internal bending radius (Ri) determined?
In air bending: Ri = V × k, where k is material-specific: mild steel 0.125, stainless 304 0.175, aluminum 0.10, high-strength steel 0.20. The internal radius is not controlled by the punch tip — it's determined by the V-die width and material springback.
What is the minimum flange length in press brake bending?
B = V × 0.656. The sheet must extend far enough to rest on both die shoulders. For a 24mm V-die: B = 15.7mm minimum. Bending with a shorter flange causes the sheet to slip into the die and produces inaccurate angles.
Air bending vs coining: which needs more force?
Coining requires 3–5× more force than air bending. Air bending is the standard method for most CNC press brakes — the punch does not bottom out and angle is controlled by depth. Coining bottoms the punch into the die for high repeatability but demands significantly more machine tonnage.
How much force does stainless steel require vs mild steel?
Stainless steel 304 (Rm 700 MPa) requires approximately 63% more force than mild steel S275 (Rm 430 MPa) for the same thickness, length, and die. For example: 2mm × 2000mm with 16mm V-die — mild steel 331 kN vs stainless 539 kN. Plan for a machine with at least 1.7× the tonnage you'd use for mild steel.
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Get Free Quote →Press brake selection and production resources
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